<html>
<head>
<title>U.S. Census TIGER/Line</title>
</head>

<body bgcolor="#ffffff">

<h1>U.S. Census TIGER/Line</h1>

TIGER/Line file sets are support for read access.  <p>

TIGER/Line files are a digital database of geographic features, such as roads,
railroads, rivers, lakes, political boundaries, census statistical boundaries,
etc. covering the entire United States. The data base contains information 
about these features such as their location in latitude and longitude, the 
name, the type of feature, address ranges for most streets, the geographic 
relationship to other features, and other related information. They are the 
public product created from the Census Bureau's TIGER (Topologically 
Integrated Geographic Encoding and Referencing) data base of geographic 
information. TIGER was developed at the Census Bureau to support the mapping 
and related geographic activities required by the decennial census and sample 
survey programs. <p>

Note that the TIGER/Line product does not include census demographic
statistics.  Those are sold by the Census Bureau in a separate format
(not directly supported by FME), but those statistics do relate back to
census blocks in TIGER/Line files.<p>

To open a TIGER/Line dataset, select the directory containing one or more
sets of data files.   The regions are counties, or county equivelents.   Each
county consists of a series of files with a common basename, and different
extentions.  For instance, county 1 in state 26 (Michigan) consists of
the following file set in Tiger98. <p>

<pre>
TGR26001.RT1
TGR26001.RT2
TGR26001.RT3
TGR26001.RT4
TGR26001.RT5
TGR26001.RT6
TGR26001.RT7
TGR26001.RT8
TGR26001.RT9
TGR26001.RTA
TGR26001.RTC
TGR26001.RTH
TGR26001.RTI
TGR26001.RTP
TGR26001.RTR
TGR26001.RTS
TGR26001.RTZ
</pre>

The TIGER/Line coordinate system is hardcoded to NAD83 lat/long degrees. 
This should be appropriate for all recent years of TIGER/Line production.<P>

There is no update or creation support in the TIGER/Line driver.<p>

The reader was implemented for TIGER/Line 1998 files, but some effort has
gone into ensuring compatibility with 1992, 1995, 1997, 1999, 2000, 2002, 2003
and 2004 TIGER/Line products as well.  The 2005 products have also been
reported to work fine.  It is believe that any TIGER/Line 
product from the 1990's should work with the reader, with the possible loss of 
some version specific information.<p>


<h3>Feature Representation</h3>

With a few exceptions, a feature is created for each record of a
TIGER/Line data file.  Each file (ie. .RT1, .RTA) is translated to an
appropriate OGR feature type, with attribute names matching those in the
TIGER/Line product manual.<p>

The TIGER/Line RT (record type), and VERSION attributes are generally
discarded, but the MODULE attribute is added to each feature.  The
MODULE attribute contains the basename (eg. TGR26001) of the county
module from which the feature originated.  For some keys (such as LAND,
POLYID, and CENID) this MODULE attribute is needed to make the key unique
when the dataset (directory) consists of more than one county of data. <p>

Following is a list of feature types, and their relationship to the 
TIGER/Line product.<p>

<h4>CompleteChain</h4>

A CompleteChain is a polyline with an associated TLID (TIGER/Line ID). 
The CompleteChain features are established from a type 1 record
(Complete Chain Basic Data Record), and if available it's associated 
type 3 record (Complete Chain Geographic Entity Codes).   As well, any
type 2 records (Complete Chain Shape Coordinates) available are used to 
fill in intermediate shape points on the arc.  The TLID is the primary
key, and is unique within the entire national TIGER/Line coverage.<p>

These features always have a line geometry.<p>

<h4>AltName</h4>

These features are derived from the type 4 record (Index to Alternate
Feature Identifiers), and relate a TLID to 1 to 4 alternate feature name
numbers (the FEAT attribute) which are kept separately as FeatureIds features.
The standard reader pipeline attaches the names from the FeatureIds
features as array attributes ALT_FEDIRS{}, ALT_FEDIRP{}, ALT_FENAME{} and
ALT_FETYPE{}.  The ALT_FENAME{} is a list of feature names associated with
the TLID on the AltName feature. <p>

Note that zero, one or more AltName records may exist for a given TLID, and
each AltName record can contain between one and four alternate names. 
Because it is still very difficult to utilize AltName features to relate
altername names to CompleteChains, it is anticipated that the standard
reader pipeline for TIGER/Line files will be upgraded in the future, resulting
in a simplification of alternate names. <P>

These features have no associated geometry.<p>

<h4>FeatureIds</h4>

These features are derived from type 5 (Complete Chain Feature Identifiers)
records.  Each feature contains a feature name (FENAME), and it's associated 
feature id code (FEAT).  The FEAT attribute is the primary key, and is
unique within the county module.  FeatureIds have a one to many relationship 
with AltName features, and KeyFeatures features.<p>

These features have no associated geometry.<p>

<h4>ZipCodes</h4>

These features are derived from type 6 (Additional Address Range and 
ZIP Code Data) records.  These features are intended to augment the
ZIP Code information kept directly on CompleteChain features, and there
is a many to one relationship between ZipCodes features and CompleteChain
features.<p>

These features have no associated geometry.<p>

<h4>Landmarks</h4>

These features are derived from type 7 (Landmark Features) records.  They
relate to point, or area landmarks.  For area landmarks there is a one to
one relationship with an AreaLandmark record.  The LAND attribute is
the primary key, and is unique within the county module.<p>

These features may have an associated point geometry.  Landmarks associated
with polygons will not have the polygon geometry attached.  It would need
to be collected (via the AreaLandmark feature) from a Polygon feature.<p>

<h4>AreaLandmarks</h4>

These features are derived from type 8 (Polygons Linked to Area Landmarks)
records.  Each associates a Landmark feature (attribute LAND) with a 
Polygon feature (attribute POLYID).  This feature has a many to many 
relationship with Polygon features.<p>

These features have no associated geometry.<p>

<h4>KeyFeatures</h4>

These features are derived from type 9 (Polygon Geographic Entity Codes) 
records.  They may be associated with a FeatureIds feature (via the FEAT
attribute), and a Polygon feature (via the POLYID attribute).  <p>

These features have no associated geometry.<p>

<h4>Polygon</h4>

These features are derived from type A (Polygon Geographic Entity Codes)
records and if available the related type S (Polygon Additional Geographic
Entity Codes) records.  The POLYID attribute is the primary key, uniquely
identifying a polygon within a county module. <p>

These features do not have any geometry associated with them as read by
the OGR TIGER driver.  It needs to be externally related using the
PolyChainLink.  The gdal/pymod/samples/tigerpoly.py script may be used
to read a TIGER dataset and extract the polygon layer <b>with geometry</b>
as a shapefile. 

<h4>EntityNames</h4>

These features are derived from type C (Geographic Entity Names) records. <p>

These features have no associated geometry.<p>

<h4>IDHistory</h4>

These features are derived from type H (TIGER/Line ID History) records.
They can be used to trace the splitting, merging, creation and deletion
of CompleteChain features. <p>

These features have no associated geometry.<p>

<h4>PolyChainLink</h4>

These features are derived from type I (Link Between Complete Chains and
Polygons) records.  They are normally all consumed by the standard reader
pipeline while attaching CompleteChain geometries to Polygon features to
establish their polygon geometries.  PolyChainLink features have a many to
one relationship with Polygon features, and a one to one relationship with
CompleteChain features. <p>

These features have no associated geometry.<p>

<h4>PIP</h4>

These features are derived from type P (Polygon Internal Point) records. 
They relate to a Polygon feature via the POLYID attribute, and can be used
to establish an internal point for Polygon features.<p>

These features have a point geometry.<p>

<h4>ZipPlus4</h4>

These features are derived from type Z (ZIP+4 Codes) records.  ZipPlus4 
features have a many to one relationship with CompleteChain features.
<p>

These features have no associated geometry.
<p>

<h3>See Also</h3>

<ul>

<li> <a href="http://www.census.gov/geo/www/tiger/">http://www.census.gov/geo/www/tiger/</a>: More information on the TIGER/Line file format, and data 
product can be found on this U.S. Census web page.<p.

</ul>

</body>
</html>
